Abstract:

By means of palinological studies realized in the pet bog Lagunas Natosas, at páramo de Jimbura, 73 taxa of pollen and spores were identified, of which 24 are the most frequent and important. Four different zones (LNT I to IV) were differentiated through cluster analysis of terrestrial pollen taxa. These data allowed the reconstruction of vegetation, including fire and climate history in the last 15,000 years BP. During the Late Pleistocene (ca. 15,000 12,000 years BP) the percentage of montane forest pollen recorded was higher in relation to the páramo, reflecting a gradual shift of this type of vegetation. This event indicates an increase in temperature during that period, causing a retreat of glaciers allowing the expansion of montane forest. In the early Holocene (ca. 12,000 – 4,800 years BP) the timberline rose, a higher percentage of Podocarpaceae, Polylepis Acaena and Hedyosmum are registered at this stage, to even greater heights than at present and, páramo vegetation was limited to 3,300–3,500 m. The climate became much warmer and wetter. Mean while the Late Holocene, about 4,800 years BP until the present, was characterized by a higher percentage of Poaceae and Cyperaceae, which are representatives of páramo vegetation. During that time, the timberline decreased, giving way to the current location of the páramo. On the other hand, the sediment record (LNT) showed that despite the fires, caused by anthropogenic activity, were much more frequent in the beginning of the Holocene, these did not affect drastically the vegetation composition at Lagunas Natosas, páramo de Jimbura.

Abstract:

A lake sediment record from Laguna Campana at 2,488 m a.s.l. in the eastern Ecuadorian Andes allows the reconstruction of local environmental conditions over the past 500 years. A high-resolution multi-proxy approach using pollen, spore, charcoal and XRF analyses provides information about lake genesis, hydrological variations and the development of the surrounding vegetation. Results suggest that Laguna Campana originated from a landslide, which are naturally common and anthropogenically promoted in the study area. Human activities, e.g. deforestation or slash and burn cultivation, impacted the local vegetation development and biodiversity during the recorded period. After a first dense layer of pioneer grasses developed on open soil around the small lake, successional stages of secondary upper mountain rainforest forest mainly composed of Alnus and Weinmannia were observed. The record shows no signs of dense forest regeneration but rather open vegetation with trees and a grassy understory. Especially since ca. A.D. 1980, the proportion of forest in the area was reduced, most probably by fire use for pastures, cultivation and wood extraction. Hydrological variability was derived from differences in minerogenic input and variations in Botryococcus braunii and Sphagnum occurrence. After wettest conditions at the study site, probably triggering the landslide, humid conditions persisted until a time of drier conditions between A.D. 1900 and 1960. A subsequent return to wetter conditions was observed over the last decades. XRF analyses suggest an increase in deposition of atmospherically derived lead since the formation of the lake.

Villota, A.; León Yánez, S. & Behling, H. (2012): Vegetation and environmental dynamics in the Páramo of Jimbura region in the southeastern Ecuadorian Andes during the late Quaternary. Journal of South American Earth Sciences40, 85-93.